The present invention relates to a method and a device for releasing a finely divided powder to be inhaled and more particularly a method and a device for releasing a medical powder from a dosing carrier connected to an inhaler for creating a well defined and efficiently inhaled medication dose.
Today supply and distribution of medical powders take place in many different ways. Within health care there is rapidly growing interest in the possibility to dose and distribute powder directly to the lungs of a patient by means of an inhaler to obtain an efficient, fast, and patient friendly administration of the specific medical substance.
In order to make certain that the medical powder to be administered will be safely carried to the lungs of a patient, the powder should have a grain size less than 5 xcexcm. Large grain sizes generally will stick in the oral cavity and the throat, and too small grain sizes may follow the expiration air out.
However, powder having a small grain size will demonstrate a strong tendency to agglomerate, i.e. to clod into larger grains. In the inhalers being used today a large portion of the powder is agglomerated when it is dosed and much powder therefore will stick to the upper respiratory tracts. Different manners to de-agglomerate the powder have been developed and in most of the cases, inspiration air is used to disassemble the agglomerated powder. Another method where de-agglomeration is performed by mechanical means is disclosed in for instance the granted Swedish Patent Application No. 9802648-7 (Swedish publication SE 512 433).
It is also common to utilize carriers having a larger grain size onto which the fine powder is distributed. Upon inspiration the large size grains will then stick in the oral cavity while the small grains will be let free and proceed to the lung. Some manufacturers also utilize electrically driven propellers, piezo-vibrators and/or mechanical vibration to disassemble the agglomerates. To obtain a large portion of separate small particles in the inspiration air is thus a very important factor to achieve a high efficiency upon inhalation.
One of the problems upon inhalation of a medical powder is that a relatively large portion of the dose will also stick in the inhaler device. To be able to include all powder and disassemble agglomerates a high air velocity is needed. However, the high velocity also has a negative influence on the emitted dose, as a large portion of the powder will stick to the walls within the inhaler. A dose given by an inhaler of today the respiratory part (grain size less than 5 xcexcm) may often be only 20% of the dose.
The problems are illustrated in U.S. Pat. No. 5,740,794 and WO 96/09085, for example, where an apparatus and a method are demonstrated for aerosolizing a medicament dose comprising dry powder to be suitable for inhalation. The applied method relies on the use of pressurized gas, normally air, for dispersing and transporting the powder and separating agglomerates into individual powder particles in the dose by using high air speeds in certain parts of the transport tube system, thereby de-agglomerating by introducing very high shear forces. Besides the inconvenience of relying on an external source of pressurized air, the evidence is far from conclusive regarding the powder retention in the powder receptacle and the transport tube system.
In order to be able to use inhalation to provide administration and in this manner replace injection of medicine the grain size must be very small. For an optimal amount of substance to reach the alveoli, an administered powder dose should preferably have an aerodynamic grain size less than 3 xcexcm. Besides, the inspiration must be carried out in a calm way to decrease air speed and thereby depositions in the upper respiratory tracts.
For achieving a high respiratory dose a so-called spacer is often used to have the small grains evenly distributed in a container from which the inhalation can take place. In principle a dosing device or an inhaler is coupled to a container having a relatively large volume and into this container a powder or an aerosol is injected, which partly is distributed in the air space and partly sticks to the walls. Upon inhalation from the spacer the fine powder floating free in the air will effectively reach the alveoli. This method in principle has two drawbacks, firstly difficulties to control the amount of medicine emitted to the lung as an uncontrolled amount of powder sticks to the walls of the spacer and secondly difficulties in handling the relatively space demanding apparatus. It has been demonstrated, e.g. in U.S. Pat. No. 5,997,848 that systemic delivery of dry insulin powder can be accomplished by oral inhalation and that the powder can be rapidly absorbed through the alveolar regions of the lungs. However, dose resolution still seems to be low. According to the disclosure, the insulin doses have a total weight from a lowest value of 0.5 mg up to 10-15 mg of insulin and the insulin is present in the individual particles at from only 5% up to 99% by weight with an average size of the particles below 10 xcexcm.
However, there is still a demand for a method and a device simplifying administration of medical powder by means of an inhaler device providing a compact arrangement without the need of, for instance, a space-demanding spacer or external power sources.
The present invention discloses a method and a device for efficiently obtaining by inhalation a total amount of administered medical powder spatially distributed in the inspiration air, preferably without the use of a so-called spacer.
According to the present method the powder is jetted off a prepared device surface containing a defined pre-metered quantity of finely divided powder, preferably an electro-powder constituting an electro-dose. The jetting function is normally the result of the inhalation effort on the user""s behalf, but in some cases the effort is aided by internal or external sources of power. By way of a user-actuated release mechanism, a directed air stream, having the characteristic of an air jet, pushes or cuts free a medical powder deposited on the surface of a carrier member. The stream of air disperses the powder and floats the individual particles into the air just as it is being inhaled. An inhaler device utilizing the present method is preferably further provided with active (air permeable) porous wall elements for further preventing powder grains from sticking to the inside faces of the inhaler device. The inhalation effort of the user creates a total pressure gradient preferably in the range 1-5 kPa over the inhaler. A part of the pressure drop is available over the active wall, thus forcing a flow of air through the active wall such that the resulting airflow prevents the floating powder particles from touching the inside faces.